1) Field of the Disclosure
The disclosure relates generally to air vehicles, and more particularly, to wing tip devices for use on air vehicles.
2) Description of Related Art
Air vehicles, such as unmanned air vehicles, solar powered aircraft, non-solar powered aircraft, high altitude air vehicles, and commercial and military aircraft, can be susceptible to atmospheric turbulence, such as wind gust loads, which can significantly overload the wings. When an air vehicle is subjected to a sudden wind gust, wind gust loads may be created on a wing or wings of the air vehicle. Such wind gust loads can cause sudden variations in the wing angle of attack which can correspondingly cause sudden variations in the wing lift and can result in wing bending that can exceed the wing load.
Devices exist that can be installed in an air vehicle wing to alleviate or reduce wind gust loads and control the wing bending resulting from such wind gust loads. For example, such devices can include wing ailerons and spoilers. Ailerons are hinged control surfaces attached to the trailing edge of a wing. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. However, such ailerons and spoilers can add weight and drag and may not be effective with air vehicles that are sensitive to added weight and drag, such as solar powered aircraft. In addition, certain air vehicles, such as solar powered aircraft, fly at very near stall, and significant wind gust loads may drive the wing into stall. Stalls in air vehicles, in particular, fixed-wing air vehicles, are often experienced when air vehicle wings produce an increased air resistance and a decreased lift as the angle of attack is increased and exceeds the critical angle of attack. A stalled wing can affect aerodynamic lift or efficiency of a wing design. It is thus desirable that a device installed to control wind gust loads be able to operate with the wing when the wing is in a stalled condition. However, ailerons and spoilers have limited effect in controlling wing bending and loading in an aerodynamically stalled environment.
Known wing tip devices, such as winglets, can be installed in the tip of a wing to increase the lift generated at the wing tip and reduce lift induced drag caused by wing tip vortices. However, winglets can add weight and drag and may not be effective with air vehicles that are sensitive to added weight and drag, such as solar powered aircraft. In addition, winglets can add to the wing's bending load, thus requiring a stronger wing which can add weight and limit flight load capability.
Accordingly, there is a need in the art for a wing tip load alleviation device and method for use on an air vehicle that provides advantages over known devices and methods.